This invention relates to systems and methods for acquiring biometric and other imagery, biometric acquisition, identification, fraud detection, and security systems and methods, particularly biometric systems and methods which employ iris recognition with a camera having a field of view. More particularly the invention relates to systems and methods for very quickly acquiring iris imagery within a wide capture volume.
Iris recognition systems have been in use for some time. The acquisition of images suitable for iris recognition is inherently a challenging problem. This is due to many reasons. As an example, the iris itself is relatively small (approximately 1 cm in diameter) and for many identification systems it is desirable to obtain a subject's iris data from a great distance in order to avoid constraining the position of the subject. This results in a small field of view and a small depth of field. Even systems which obtain iris data from a close in subject must be adapted to subjects which do not stay absolutely still. Systems must also deal with subjects which blink involuntarily or drop or swivel their head momentarily to check on the whereabouts of luggage.
There is therefore a need to scan very quickly or else the person will have moved out of the capture volume or the subject's motion will cause a blur. In the current state of the art, attempts to resolve this problem comprise using a flat mirror to scan but such attempts have not so far resolved the motion blur problem, especially when the camera is zoomed in. The image motion in terms of pixels/second is very high which makes it very difficult to obtain high quality imagery with prior art systems in these situations.
In biometric applications, one or more image sensors are often used to collect data for subsequent analysis and biometric matching. For example, with the face or iris biometric, a single camera and lens is often used to collect the biometric data. There is an obvious trade-off between the resolution required for biometric analysis and matching, and the field of view of the lens. For example, as the field of view of the lens increases, the capture volume or coverage in which the biometric data can be observed increases, but the resolution of the data decreases proportionally. Multiple cameras and lenses covering a larger volume is an obvious solution, but it requires the expense of additional cameras, optics and processing.
Another approach for increasing the capture volume has been to use controllable mirrors that point the camera coverage in different locations. Specifically, in U.S. Pat. No. 6,714,665 it is proposed to use a wide field of view camera to determine where to point a mirror that was mounted on a pan/tilt/zoom assembly. However approaches that point mirrors in such a fashion have to handle one or more key problems, namely: (i) the time latency involved in moving the camera to a location, (ii) vibration of the mirror and the resulting settling time of the mirror as it stops and starts motion, (iii) the complexity of the mechanical arrangement, (iv) the reliability, longevity and expense of the opto-mechanical components for such a moving assembly.
U.S. Pat. No. 6,320,610, Van Sant et al disclosed acquisition of biometric data with a mirror on a pan/tilt platform, or a camera on pan/tilt platform. The problem with that approach is that it is very expensive or physically impossible to use such a mechanism to point at 2 or 3 places in a scene at a very high rate—for example, 5-50 times a second. If there is a mechanical mirror or pointing mechanism, then there is substantial inertia preventing the rapid stopping and starting of the assembly quickly and furthermore such a system needs a very powerful actuator/motor to rotate a camera assembly. In addition, there is substantial settling time for the mirror or camera to stop vibrating as the mirror or pan/tilt assembly stops before imagery is acquired, so essentially it makes it almost physically impossible to scan at such high rates.